Photothermal conversion material and preparation method and application thereof

Abstract

The invention relates to a photothermal conversion material. The photothermal conversion material is a CsSnI3-loaded mesoporous material with a core-shell structure, wherein the CsSnI3 perovskite quantum dot is used as a quantum dot core, and the mesoporous material is used as a shell layer to coat the quantum dot core; the surface of the CsSnI3 perovskite quantum dot has high defect density, the fluorescence quantum yield (PLQY) of the CsSnI3 perovskite quantum dot is less than 2%, and the average fluorescence lifetime of the CsSnI3 perovskite quantum dot is less than 2ns; the photo-thermal conversion efficiency (PCE) of the photo-thermal conversion material is greater than or equal to 94%. The photo-thermal conversion material has the characteristics of high photo-thermal conversion efficiency, strong light absorption and high stability, and can be applied to the field of illumination heat collection.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photothermal materials, and particularly relates to a photothermal conversion material and a preparation method and application thereof. BACKGROUND

[0002] A photothermal material is a material that converts light energy into heat energy, and has been widely researched and applied in the fields of medicine, environment, energy and communication, such as photothermal therapy, seawater evaporation, light sensing, etc. Among them, the solar water evaporation technology is inspired by natural evaporation, based on photothermal conversion materials, and uses the local high heat generated by the absorption of photons by photothermal conversion materials to heat the surrounding water. After the water molecules evaporate and recondense, fresh water resources can be obtained. Through this technology, seawater desalination, sewage purification, wastewater treatment and other goals can be achieved. Therefore, the performance of the photothermal material is very important in the seawater desalination device.

[0003] At present, although significant progress has been made in the research and development of advanced materials such as metal nanostructures, semiconductors, carbon-based nanomaterials and organic polymers, there are still key challenges: materials such as Au and Ag face the problems of limited solar absorption range and high synthesis cost; traditional semiconductors are prone to photon radiation due to their wide bandgap characteristics, resulting in low photothermal conversion efficiency; carbon-based nanomaterials such as graphene have cyclic thermal instability; organic polymers such as organic hydrogels are limited by high temperature resistance and large-scale preparation problems. Therefore, an ideal photothermal material must have excellent photothermal performance, economic feasibility and long-term stability under harsh working conditions.

[0004] Metal halide perovskite materials have excellent light absorption coefficient, adjustable band gap and economic and efficient preparation process, so there is an objective basis for their application in photothermal conversion materials and photoelectric conversion materials (both rely on high absorption of light). However, the two have different ways of converting energy after absorbing light, which can be summarized as follows:

[0005] (1) Currently applied in the field of perovskite solar cells. Its photoelectric conversion mechanism is as follows:

[0006] Metal halide perovskite generates electron-hole pairs after absorbing photons, which are separated under the driving of the built-in electric field to form a current output. Under this mechanism, it relies on the separation and directional migration of photo-generated carriers. Secondly, in terms of heat management mechanism, it is necessary to dissipate heat as soon as possible to slow down the decay of photoelectric conversion efficiency (85℃ aging for 500h, device failure risk >40%).

[0007] (2) If the metal halide perovskite material is used in the field of photothermal materials, the photothermal conversion mechanism (non-radiative relaxation dominant) used is as follows:

[0008] After the metal halide perovskite absorbs photons, the excited state electrons release heat energy through phonon scattering (lattice vibration). Under this mechanism, it is necessary to reduce the carrier directional migration as much as possible. Secondly, in the heat management mechanism, it is necessary to store heat as much as possible to inhibit heat dissipation.

[0009] It is precisely because there is an essential conflict between photothermal materials and photoelectric materials in technical principles that the metal halide perovskite material currently implemented in photoelectric conversion cannot be directly technically transplanted into photothermal materials, and there is a technical obstacle. At the same time, the current metal halide perovskite material lacks empirical research in the application of photothermal conversion materials, and therefore needs to be improved. SUMMARY

[0010] The application provides a kind of photothermal conversion material and its preparation method and application based on it. The photothermal conversion material has the characteristics of high photothermal conversion efficiency, strong light absorption and high stability, and can be applied to the field of light heat collection (including but not limited to seawater evaporation).

[0011] To achieve the above purpose, the technical scheme adopted by the application is:

[0012] A kind of photothermal conversion material, the photothermal conversion material is CsSnI3 mesoporous material with core-shell structure;

[0013] Wherein, CsSnI3 perovskite quantum dots are used as quantum dot cores, and mesoporous materials are used as shell layers to coat the outside of the quantum dot cores. The CsSnI3 perovskite quantum dot surface has a high defect density, a fluorescence quantum yield (PLQY) of less than 2%, and an average fluorescence lifetime of less than 2ns.

[0014] The photothermal conversion efficiency (PCE) of the photothermal conversion material is greater than or equal to 94%.

[0015] Further, the ligand-free surface of CsSnI3 in the photothermal conversion material induces non-radiative recombination of photo-generated carriers. That is, the surface of the CsSnI3 perovskite quantum dots does not have ligands or passivation layers to passivate defects.

[0016] Further, the high defect density of the CsSnI3 perovskite quantum dot surface can be induced to be exposed, and the induced CsSnI3 perovskite quantum dots exhibit at least two or three of the following scenarios:

[0017] (1) PLQY drops sharply (<2%);

[0018] (2) the average fluorescence lifetime is shortened to <2ns;

[0019] (3) XPS appears Sn 4+ or surface halogen vacancy signal;

[0020] (4) Auger recombination induced power-dependent nonlinear fluorescence quenching.

[0021] In the above, Sn 4+ The appearance of Sn means that part of the divalent tin is oxidized to tetravalent tin, and then tin vacancies appear. The appearance of tin vacancies or iodine vacancies means the exposure of surface defects of CsSnI3 perovskite quantum dots. The explanation of the serial number (4) is as follows: when the excitation power increases, the carrier density in the quantum dot increases, and the probability of Auger process (exciton + additional electron or hole) increases sharply, so that the fluorescence no longer increases linearly with the power, but appears "the darker the more light" nonlinear quenching.

[0022] Further, the mesoporous material has high specific heat capacity and low thermal conductivity; specifically, the specific heat capacity of the mesoporous material is greater than the specific heat capacity of the CsSnI3 perovskite quantum dot.

[0023] The mesoporous material is one of mesoporous molecular sieves, mesoporous silica, glass, mesoporous titanium dioxide, mesoporous aluminum oxide, mesoporous carbon, mesoporous transition metal oxide, mesoporous sulfide, mesoporous silicate, mesoporous aluminate or mesoporous transition metal nitride.

[0024] A preparation method of a light-heat conversion material, comprising the following steps:

[0025] S1, mixing: mixing perovskite nanocrystal precursor and mesoporous material to obtain a mixture, the perovskite nanocrystal precursor is composed of CsI and SnI2;

[0026] S2, primary calcination synthesis: heating to a first calcination temperature and holding, calcining the mixture obtained in step S1 in an inert atmosphere;

[0027] S3, secondary calcination induction: continuing to heat to a second calcination temperature and holding based on step S1 to promote the closure of the mesoporous material; then rapidly cooling the product after secondary calcination to room temperature to obtain the light-heat conversion material.

[0028] Further, the molar ratio of SnI2 to CsI in the perovskite nanocrystal precursor is at least 3:1, so as to provide excess SnI2 as a reaction raw material.

[0029] Further, the second calcination temperature is greater than the first calcination temperature, and the second calcination temperature is greater than the pore collapse temperature of the mesoporous material.

[0030] The first calcination temperature is 350-500℃.

[0031] Further, the step S3 adopts a three-stage thermodynamic disturbance of "high temperature-hysteresis-quenching", to induce high defect density on the surface of CsSnI3 perovskite quantum dots.

[0032] Further, the second calcination temperature is at least 650 DEG C, corresponding to "high temperature";

[0033] The holding at the second calcination temperature is for at least 30 min, corresponding to "delay";

[0034] The product after the secondary calcination is rapidly cooled in air or water, corresponding to "quenching".

[0035] By adopting the technical scheme, the "high temperature-delay-quenching" three-stage thermodynamic disturbance is adopted in the step S3, high defect density is induced on the surface of the CsSnI3 perovskite quantum dot, and then the perovskite is caused to release as much heat energy as possible through phonon scattering (lattice vibration) of the excited state electrons after absorbing photons, so that the optimal photo-thermal conversion efficiency (PCE) of the photo-thermal conversion material is greater than or equal to 99%.

[0036] The high-temperature stage (greater than 650 DEG C) in the secondary calcination is used to promote the mesoporous material to close the pores as much as possible, so that the pore channels collapse to coat the CsSnI3. At this time, the CsSnI3 is protected by the external mesoporous material and has the ability to block water and oxygen, thereby improving the stability of long-term application. On the other hand, the high-temperature stage (greater than 650 DEG C) can induce the surface defects of the CsSnI3 to be exposed as much as possible.

[0037] The holding stage in the secondary calcination can prolong the high-temperature residence time, promote the defect chemical potential of the halogen vacancies and metal dangling bonds on the surface of the CsSnI3 to continuously increase, and realize the dynamic accumulation of the defect density.

[0038] In the quenching stage in the secondary calcination, a large number of crystal nuclei are generated due to the large supercooling degree in the rapid cooling process, but the cooling speed is too fast to be conducive to the growth of the crystal, so that the CsSnI3 nanocrystal particles are small, the grain boundary density is high, and more defects are generated.

[0039] An application of the photo-thermal conversion material in the fields of seawater desalination, building heating energy saving, agricultural greenhouse regulation and light harvesting.

[0040] The application has the beneficial effect that a composite material CsSnI3 mesoporous material is developed, which can be used in the field of seawater desalination. The photo-thermal material has a large absorption cross section, a high defect density, a high photo-thermal conversion efficiency and super-strong stability.

[0041] In existing technologies, reported γ-CsSnI3 materials are mostly used in optoelectronic devices such as solar cells and LEDs, where incident light energy is released primarily as photons rather than heat. Furthermore, γ-CsSnI3 is typically synthesized via solution methods or co-evaporation, and surface defects are passivated through additives or ligand engineering, resulting in high performance-to-quality ratio (PLQY). However, photothermal materials require stable heat output under long-term high-temperature and high-humidity environments (such as in seawater desalination), and the perovskite structure itself is susceptible to damage from light, heat, water, and oxygen. Therefore, the application of γ-CsSnI3 in photothermal materials faces challenges. This invention achieves the application of γ-CsSnI3 in photothermal materials through the following approach:

[0042] (1) CsSnI3 has a narrower band gap, extending its absorption range into the near-infrared region; on the other hand, it has lower defect tolerance, which makes photogenerated carriers more prone to nonradiative recombination and dissipate energy as heat rather than light. Furthermore, as... Figure 1 As shown in a, this structure, which consists of silicon oxide coated with multiple nanocrystals, allows light to undergo multiple reflections and refractions within the matrix, thereby enhancing light absorption.

[0043] (2) This invention utilizes high-temperature calcination to introduce high-density surface defects into the CsSnI3@mesoporous material, almost completely closing the CsSnI3 radiation channels. This allows more than 90% of the photoexcitation energy to be converted into phonon heat within the picosecond-nanosecond timescale. Combined with a high specific surface area and a controllable thermal diffusion shell (mesoporous material), a high heat conversion efficiency is ultimately achieved. Mesoporous materials possess the characteristics of high specific heat capacity and low thermal conductivity, serving as both a water-oxygen barrier and a heat-accumulating and heat-storing barrier. Attached Figure Description

[0044] Figure 1 (a) is a diagram of the photothermal effect mechanism of the photothermal conversion material CsSnI3@mesoporous material prepared in Example 1 of the present invention; Figure 1 (b) is 0.3 W / cm 2 The average photothermal temperature-time curves of CsSnI3@silica (Example 1) compared with those of commercial graphene, indocyanine green, and CsSnI3 (Comparative Example 7) within one cycle of 808nm laser irradiation and shutdown. Figure 1 (c) Under the same power 808nm laser excitation Figure 1 (b) Thermal images of the four materials shown; Figure 1 (d) is the photothermal temperature curve of CsSnI3@Sillica in Example 1 as a function of incident light intensity. Figure 1 (e) is the output time-temperature curve of the CsSnI3@Sillica cyclic on-off test in Example 1; Figure 1(f) is the stability test curve of CsSnI3@Silica (Example 1) / CsSnI3 (Comparative Example 7) / Graphene;

[0045] Figure 2 is the XRD pattern of the phase obtained by precursor ratio adjustment of Example 1, Comparative Example 8, Comparative Example 9;

[0046] Figure 3 (a) is the photo-thermal conversion efficiency (PCE) and the maximum photo-thermal temperature when reaching thermal equilibrium under 808 nm laser irradiation of 0.3 W / cm2of Examples 1-7; 2 Figure 3 (b) is the fluorescence quantum yield (PLQY) of Examples 1-7; Figure 3 (c) is the specific heat capacity data of the materials, red is CsSnI3with silica coating (Example 1), and black is CsSnI3without silica coating; Figure 3 (d) is the fluorescence lifetime decay curve of Examples 1-3;

[0047] Figure 4 is the temperature cooling curve (temperature-time curve) of the photo-thermal conversion material CsSnI3@mesoporous material prepared in Example 1 after the 808 nm excitation light is turned off, wherein the red curve is fitted by formula (2);

[0048] Figure 5 is the (a) water evaporation mass change; (b) water evaporation rate within 30 min when the photo-thermal fiber of Application Example 10 is applied to seawater desalination. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and effects of the present application more clear and explicit, the present application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0050] The mesoporous material includes but is not limited to one of mesoporous molecular sieve, mesoporous silica, glass, mesoporous titanium dioxide, mesoporous aluminum oxide, mesoporous carbon, mesoporous transition metal oxide, mesoporous sulfide, mesoporous silicate, mesoporous aluminate or mesoporous transition metal nitride. The mesoporous material in the following examples of the present application is selected as MCM-41 silica material for illustration, which does not constitute a limitation to the mesoporous material in the present application. The mesoporous material in the present application not only acts as a water and oxygen barrier but also as a heat trapping barrier, and the specific heat capacity of the mesoporous material is greater than that of the CsSnI3perovskite quantum dot. As long as under this inventive concept, any mesoporous material selected by those skilled in the art should be within the protection scope of the present application.

[0051] Example 1:

[0052] ​Select CsI for 1 mmol, that is, 260 mg, SnI2 for 3 mmol, that is, 1118 mg, and MCM-41 for 1378 mg for blending, manually grind for 5 min, and then put into a porcelain boat with a cover. Put the porcelain boat into a tube furnace, introduce argon, and use a vacuum pump to extract the gas in the tube. After repeating the extraction and charging three times, start calcination under an argon atmosphere, calcine at 450°C for 60 min, calcine at 650°C for 60 min, and then cool down with the furnace.

[0053] Example 2:

[0054] The difference from Example 1 is that the holding time of the second calcination is changed from calcination at 650°C for 60 min to calcination at 650°C for 30 min.

[0055] Comparative Example 3:

[0056] The difference from Example 2 is that the calcination atmosphere is modified as follows.

[0057] Start calcination under an argon atmosphere is replaced by: start calcination under a mixed atmosphere of argon and I2. The role of the I2 atmosphere is to provide an I-rich environment to fill the I vacancies that appear in CsSnI3.

[0058] Conclusion: As shown in Table 1, passivation of surface defects on the surface of CsSnI3 (for example, to fill I vacancies) can improve the PLQY, but will reduce the PCE. Figure 3

[0059] Comparative Example 4:

[0060] The difference from Example 1 is that there is no first calcination temperature. Specifically as follows:

[0061] The preparation before calcination is the same as in Example 1. Calcine under an argon atmosphere, directly heat up to 650°C at a rate of 10°C / min for 60 min, and then cool down with the furnace.

[0062] Conclusion: As shown in Table 1, since there is no holding process at the first calcination temperature, the direct calcination heating rate is too fast to be conducive to the formation of CsSnI3 through the full reaction of the precursor. Figure 3

[0063] Comparative Example 5:

[0064] The difference from Example 1 is that the second calcination temperature is changed from 650°C to 600°C. The others remain unchanged.

[0065] Conclusion: As shown in Table 1, since the second calcination temperature is changed from 650°C to 600°C, the PCE is reduced. Figure 3 ​​As shown, since the collapse temperature of mesoporous silica is 600℃, the MCM-41 has actually completed the collapse of the pores at the second calcination temperature of 600℃, so that the shell layer MCM-41 can block the water and oxygen. However, we found that continuing to increase the second calcination temperature helps to generate surface defects of CsSnI3, thereby improving the photo-thermal conversion efficiency PCE.

[0066] Example 6:

[0067] The difference from Example 2 is that the furnace cooling method is replaced by taking the product out of the tube furnace and rapidly cooling it in air.

[0068] Conclusion: As shown in Figure 3 , the cooling speed of Example 6 is faster, and a large number of crystal nuclei are generated due to the large supercooling degree during the rapid cooling process, but the cooling speed is too fast to be conducive to the growth of the crystal, so the CsSnI3 nanocrystal particles are small, the grain boundary density is high, and more surface defects are generated.

[0069] Comparative Example 7:

[0070] CsI is taken as 1 mmol and SnI2 is taken as 3 mmol for blending and grinding, and the preparation before calcination is the same as Example 1. It is calcined under an argon atmosphere, calcined at 350℃ for 12h, and then cooled in the furnace to obtain CsSnI3 nanocrystals without silica coating.

[0071] Conclusion: As shown in Figure 3 , since Comparative Example 7 lacks silica coating, it cannot stably isolate the destruction of external water and oxygen to CsSnI3. Further analysis shows that: because the specific heat capacity of silica is large and the thermal conductivity is low, it plays a heat preservation role; the nano structure of silica coated CsSnI3 can make the incident light multiple scattering and refraction in CsSnI3@Silica, the light penetration depth is deeper, the optical path is longer, and the light absorption is improved

[0072] Comparative Example 8:

[0073] The difference from Example 1 is that the molar ratio of CsI to SnI2 is adjusted to 1:2, and the rest is the same as Example 1.

[0074] Comparative Example 9:

[0075] The difference from Example 1 is that the molar ratio of CsI to SnI2 is adjusted to 1:1, and the rest is the same as Example 1.

[0076] Conclusion: As shown in Figure 2 , when SnI2:CsI = 1:1 or 2:1, γ-CsSnI3 cannot be obtained, and when SnI2:CsI = 3:1, γ-CsSnI3 with clear peak type is obtained.

[0077] The application synthesizes CsSnI3@silica nanocrystals with surface underpassivation and high defect density by high-temperature calcination. Thus, based on this specific synthesis process, the composition ratio of the specific perovskite precursor is provided.

[0078] Application Example 10:

[0079] PC master batch (60 g), titanium white (0.42 g), diffusion powder (0.9 g), CsSnI3@silica powder prepared in Example 1 (0.045 g), and calcium stearate (0.15 g) are uniformly mixed, and then melt-extruded at 200 DEG C into light-heat fibers with a diameter of about 0.5 mm. Under the irradiation of one sunlight, the evaporation mass change and evaporation rate of the obtained light-heat fibers within 30 min are shown in Figure 5 .

[0080] In the application Figure 1 (b), the information of the commercial graphene and indocyanine green used is as follows:

[0081] Flaky graphene: CAS No. 7782-42-5, brand: Mclane, purity > 90%, industrial grade.

[0082] New indocyanine green: CAS No. 172616-80-7, brand: Mclane, analytical pure AR.

[0083] The photothermal performance and principle of the CsSnI3@mesoporous material of the application are introduced as follows:

[0084] As shown in Figure 3 , the PLQY of the CsSnI3@mesoporous material obtained by the application is less than 2%. This is far less than the colloidal CsSnI3 nanocrystals (18.4%) reported in the existing literature. These results show that the ligand-free surface of CsSnI3 in the CsSnI3@mesoporous material induces significant non-radiative recombination of photo-generated carriers. Through the photothermal conversion efficiency η calculation formula (1):

[0085]

[0086] Where c is the specific heat capacity, m is the mass, Tmax and Tsurr are the highest temperature and stable ambient temperature at thermal equilibrium, respectively, I is the incident light intensity, a is the incident light absorption rate, and τs is the time constant. The cooling curve in formula 2 can be fitted to obtain Tmax, Tsurr, and τs required in formula 1: Figure 4 .

[0087]

[0088] We measured the photothermal conversion efficiency of the material under 808 nm near-infrared light irradiation (the calculation process is as follows: Figure 4As shown in the figure, its value is as high as 99.4%, proving that the material can convert most of the absorbed near-infrared photons into heat energy. At the same power (0.3 W / cm²), 2 Under 808nm laser irradiation ( Figure 1 (bc) We compared the average surface temperatures of CsSnI3@silica composites, commercial graphene sheets, commercial photothermal dyes (neoindocyanine green), and unencapsulated CsSnI3 powder. The results showed that the CsSnI3@silica system achieved the highest average temperature of 40.7℃, which was superior to graphene (40.3℃), neoindocyanine green (37.8℃), and CsSnI3 powder (32.2℃).

[0089] Figure 1 Figure d illustrates the variation of the material's maximum surface temperature under irradiation with different powers of 808nm laser: when the incident light power density reaches 0.6W / cm²... 2 At this point, the surface temperature can reach a maximum of 94℃. This also indicates that under variable power excitation, the material reaches different photothermal temperatures, demonstrating a power-dependent relationship.

[0090] Figure 1 The time-varying photothermal response curves recorded by e indicate that the material exhibits highly stable and repeatable photothermal response characteristics during near-infrared light switching cycles.

[0091] See Figure 1 f. We further compared the photothermal stability of the three materials in an accelerated aging environment: Under high humidity (85% relative humidity, 85℃), CsSnI3@silica maintained 90.1% of its initial performance (meaning the average photothermal temperature achievable under the same excitation power density) after 30 days of aging, while graphene / CsSnI3 powder decreased to 75.4% / 61.9% respectively after 1 week of aging; Under high temperature (250℃), CsSnI3@silica maintained 90.4% of its performance after 50 days of aging, while graphene / CsSnI3 powder decreased to 76.6% / 64.2% respectively after 1 week of aging; Under strong light irradiation (808nm, 6W / cm²), the performance was further compared. 2 Under the condition of 4 days, CsSnI3@silica showed no significant degradation, while graphene / CsSnI3 powders showed degradation to 82.2% / 61.7% respectively during the same period.

[0092] The present invention has been illustrated with the above embodiments to explain the detailed preparation method of the present invention. However, the present invention is not limited to the above detailed preparation method, that is, it does not mean that the present invention must rely on the above product and detailed preparation method to be implemented. Those skilled in the art should understand that any improvement to the present invention, or the combination or equivalent substitution of the raw materials of the present invention, falls within the protection scope and disclosure scope of the present invention.

Claims

1. A photothermal conversion material, characterized in that, The photothermal conversion material is a CsSnI3@mesoporous material with a core-shell structure; CsSnI3 perovskite quantum dots are used as the quantum dot core, and mesoporous materials are used as the shell to coat the quantum dot core. The CsSnI3 perovskite quantum dots have a high defect density, a fluorescence quantum yield (PLQY) of <2%, and an average fluorescence lifetime of <2ns. The photothermal conversion efficiency (PCE) of the photothermal conversion material is ≥94%.

2. The photothermal conversion material according to claim 1, characterized in that, The ligand-free surface of CsSnI3 in the photothermal conversion material induces nonradiative recombination of photogenerated carriers.

3. The photothermal conversion material according to claim 2, characterized in that, The high defect density on the surface of the CsSnI3 perovskite quantum dots can be induced to be exposed, and the induced CsSnI3 perovskite quantum dots exhibit at least two or three of the following scenarios: (1) PLQY dropped sharply (<2%); (2) The average fluorescence lifetime is shortened to <2ns; (3) XPS shows Sn 4+ Or surface halide vacancy signal; (4) Power-dependent nonlinear fluorescence quenching caused by Auger recombination enhancement.

4. The photothermal conversion material according to claim 1, characterized in that, The mesoporous material is one of the following: mesoporous molecular sieve, mesoporous silica, glass, mesoporous titanium dioxide, mesoporous alumina, mesoporous carbon, mesoporous transition metal oxide, mesoporous sulfide, mesoporous silicate, mesoporous aluminate, or mesoporous transition metal nitride.

5. A method for preparing a photothermal conversion material according to claims 1-4, characterized in that, Includes the following steps: S1. Mixing: The perovskite nanocrystal precursor and the mesoporous material are mixed to obtain a mixture, wherein the perovskite nanocrystal precursor is composed of CsI and SnI2; S2, one-time calcination synthesis: heat to the first calcination temperature and hold at that temperature, calcining the mixture obtained in step S1 in an inert atmosphere; S3, Secondary Calcination Induction: Based on step S1, the temperature is further increased to the second calcination temperature and held to promote the pore closing of the mesoporous material; then the product after secondary calcination is rapidly cooled to room temperature to obtain the photothermal conversion material.

6. The method for preparing a photothermal conversion material according to claim 5, characterized in that, The molar ratio of SnI2 to CsI in the perovskite nanocrystal precursor is at least 3:

1.

7. The method for preparing a photothermal conversion material according to claim 5, characterized in that, The second calcination temperature is greater than the first calcination temperature, and the second calcination temperature is greater than the pore collapse temperature of the mesoporous material; The first calcination temperature is 350-500℃.

8. The method for preparing a photothermal conversion material according to claim 5, characterized in that, In step S3, a three-stage thermodynamic perturbation of "high temperature-delay-quench" is used to induce a high defect density on the surface of CsSnI3 perovskite quantum dots.

9. The method for preparing a photothermal conversion material according to claim 8, characterized in that, The second calcination temperature is at least 650°C, corresponding to "high temperature"; The second calcination temperature is maintained for at least 30 minutes, corresponding to "delay". The product after secondary calcination is rapidly cooled in air or water, which corresponds to "quenching".

10. The application of a photothermal conversion material as described in any one of claims 1-4 in the fields of seawater desalination, building heating energy conservation, agricultural greenhouse regulation, and solar thermal collection.

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